The invention relates to a bone anchoring device for anchoring a stabilization rod in a bone or in a vertebra, an assembly tool and a method for assembling the bone anchoring device and an insertion tool for use with the bone anchoring device. The bone anchoring device includes an anchoring element, a receiving part for receiving a head of the bone anchoring element and for receiving a stabilization rod to be connected to the anchoring element. The anchoring element is pivotably connected to the receiving part and can be fixed at an angle by exerting pressure onto the head via a pressure element, which is arranged in the receiving part. The pressure element comprises a spring element that engages a portion of the receiving part so that it can be held in a position that allows pivoting of the anchoring element.
U.S. Pat. No. 5,716,356 describes a polyaxial bone screw including a screw element and a receiving part that is pivotably connected to the screw element and a pressure element to exert pressure onto the head of the screw element to fix the angle between the screw element and the receiving part. The receiving part has an U-shaped channel for receiving a stabilization rod. The pressure element comprises a cylindrical recess which is to be aligned with the U-shaped channel to receive the rod therein. In order to hold the pressure element in a position aligned with the U-shaped channel, the position of the pressure element is fixed by crimping through bores provided in the receiving part.
U.S. Pat. No. 5,672,176 describes another example of a polyaxial bone screw with a pressure element that is also held in place by crimp bores without impeding a sufficient movement of the pressure element to clamp the head.
US 2005/0080420 A1 describes a multiaxial bone screw that includes a screw element and a receiver member, a base member for retaining the screw element in the receiver member and a crown element exerting pressure onto the head of the screw element. The crown element comprises a snap-ring to assist in holding the crown element within the receiving part by interfering with a stop surface of the receiving part. The multiaxial bone screw is a so-called bottom loading type screw wherein the screw element is introduced from the bottom into receiving part.
WO 2006/116437 A2 describes a bone anchor for spinal fixation in the form of a polyaxial bone screw including a screw element, a housing, a sleeve and a collet arranged in the housing for exerting pressure onto the head of the screw element. The sleeve has retention tabs that snap into slots in opposite wall positions of the housing.
Usually, the polyaxial bone screws of the above-described type are delivered, for example by the manufacturer, in a pre-assembled condition. In this condition a specific screw element, e.g. a screw element having a specific length and shaft diameter or a specific thread form, is connected to a receiving part and the pressure element is arranged therein so that it cannot escape. For the surgery, the necessary number and types of such pre-assembled polyaxial bone screws are selected and provided in advance as a full set of implants.